Downy mildew
| Downy mildew | |
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| A grape leaf showing downy mildew and powdery mildew | |
| Scientific Classification | |
| Kingdom: | Chromalveolata |
| Phylum: | Heterokontophyta |
| Class: | Oomycetes |
| Order: | Peronosporales |
| Family: | Peronosporaceae |
Downy mildew refers to any of several types of oomycete microbes of the Peronosporaceae family that are a particular problem for growers of brassicas, grapes and vine-type vegetables.
Cucurbit downy mildew (caused by Pseudoperonospora cubensis) is specific to cucurbits (e.g. pumpkin, squash, courgette). The disease is one of the most important diseases of cucurbits worldwide.
A serious disease in cool, damp seasons.
Symptoms[edit | edit source]
The initial symptoms of downy mildew appear on leaves as light green to yellow spots, then as it develops it becomes a downy grey mould. Leaves slowly die back and shrivel from the tips.[1] Onion bulbs infected become soft and are not suitable for storage.
Treatment[edit | edit source]
None. Should the disease be confirmed on site, immediately dispose of diseased material in sealed bags or bins and arrange for it to be destroyed.[2]
Prevention[edit | edit source]
Good practice[2]:
- Try to ensure any starting plant material is disease free.
- Provide good air circulation and ventilation in glasshouses.
- Try to avoid long periods of high humidity and leaf wetness.
- Avoid watering crops late in the day.
- Apply a routine preventative fungicide programme to minimise disease risk, especially during periods when environmental conditions are favourable for downy mildew infection.
- Practice good nursery hygiene by cleaning up plant debris between crops and at the end of the season and use appropriate disinfectants.
Examples[edit | edit source]
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Broccoli (Peronospora parasitica)
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Cucumber (Pseudoperonospora cubensis)
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Grape leaf (Plasmopara viticola)
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Lettuce (Bremia lactucae)
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Onion (Peronospora destructor)
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Parsley (Peronospora umbelliferarum)
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Raspberry (Peronospora sp.)
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Sage (Peronospora lamii)
References[edit | edit source]
- ↑ Hessayon, D.G. (2009). The Vegetable & Herb Expert. Transworld Publishers, London. p. 75. ISBN 9780903505468
- ↑ a b McPherson, M. and Brough, W. (2009) "Good Horticultural Practice for the Prevention and Control of Impatiens Downy Mildew (Plasmopara obducens)". Agriculture and Horticultural Development Board. Retrieved 2010-07-17.
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| Lettuce troubles |
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| Adverse conditions | Bolting · Calcium deficiency · Phosphorus deficiency |
| Diseases | Aster yellows · Bacterial leaf spot of lettuce · Bidens mottle virus · Downey mildew · Grey mould · Lettuce infectious yellows virus · Sclerotinia rot |
| Pests | Aphid · Cutworm · Flea beetle · Root-knot nematode · Slug |
| Mint troubles |
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| Basil · Lavender · Lemon balm · Marjoram · Mint · Oregano · Rosemary · Sage · Savory · Thyme | |
| Adverse conditions | Bolting |
| Diseases | Bacterial leaf spot of endive · Downy mildew · Fusarium wilt · Grey mould · Powdery mildew · Rhizoctonia solani · Rust · Septoria leaf spot of lemon balm · Verticillium wilt |
| Pests | Aphid · Cabbage whitefly · Capsid bug · Celery fly · Leaf miner · Leafhopper · Red spider mite · Shore fly · Silver Y moth · Slug |
